Lost Kesubah

If a couple lost their kasubah would a copy ('tzilum') of it suffice? (i.e. in terms of issur yichud or for any other purpose.)

Answer:

A copy of the kesubah is proof of the fact that there was a kesubah. However, because the original is missing, this will not suffice, because the husband will be able to claim that he paid the kesubah after a divorce, and the copy won't refute his claim. Under such circumstances, a kesubah is not valid (see Kesubos 57; Even Ha-Ezer 66:3).

Yet, if the husband will countetrsign the kesubah, indicating that the kesubah is a faithful copy of a lost kesubah, he will no longer be able to claim that the kesubah has been paid, and the copy will serve as a valid kesubah for all intents and purposes.

Although the sefer Kesubah Kehilchasah writes that one should write a kesubah de'irkesah (a special nusach for a case where a kesubah was lost), the option above appears fine, and I saw that this is the advice given in Lev Aryeh (Grosnass, no. 42).